Sunday, November 25, 2012

Shaking fur science: How animals shed water by shaking

When an animal shakes water off its fur, it may look like a simple instinctive action. But the hand of evolution has optimised fur shakes across the hairy mammals so they don't waste energy.

Shake it off! Photo credit: AllPosters.com

Using a hosepice and spray bottle, researchers at Georgia institute of Technology in the US soaked 33 animals obtained from zoo, a lab and a local park, and use a high-speed camera to film at up to 1,000 frames per second as they shook away the water.

Mouse movement: Mice remove 70% of the water in their coats in less than 1 second.

Shake speed

Animal shake speed (frequency) shown in Hertz, is fastest in mice, i.e. 29Hz. To define it, a 1 Hz shaking speed means an animal shakes once every second. This means, a mouse can shake 29 times in a single second. The following list compares the speed of different animals:

Mouse - 29Hz

Cat - 9.4Hz

Pig - 8.2Hz

Kangaroo - 4.9Hz

Lion - 4.8Hz

Labrador - 4.3Hz

Bear - 4Hz

Removing water from fur restores its power of insulation. But to do this, an animal needs to overcome the surface tension between the water and the hair. So its shake must generate sufficient centrifugal force. In a shake, centrifugal force increases with distance from the centre of the animal, which means smaller animals have to compensate, shaking harder, to shift the same amount of water as large animals.

What's the benefit of knowing all this?

Isn't that seem a bit silly for scientists to study the way an animal shakes itself dry? Maybe, but it could help engineers come up with automated-cleaning techniques to use in devices we can’t easily clean ourselves, such as the insides of cameras or distant space rovers.

Also, a better understanding of the relationship between shaking and the removal of droplets could help engineers with the design of everything from washing machine to painting devices.